When you don't convert the loft into a living space and keep the loft cold you can opt for loft joist insulation. This keeps the house warm and the loft in close to original state. The benefit of choosing a cold roof over a warm roof is that this type of insulation can be layed on in a thick layer and cheaper material can be used for insulation. The cost are also kept down because laying insulation on the loft floor requires less material than insulation the pitched roof.
As loft conversion experts we don't deal with this type of insulation often. We do this when a loft conversion is simply not possible and home owners want to save on the heathing bills. The savings from this type of insulation can be won back in just a few years. It also adds value to the property as loft insulation is one of the main items that help to increase your EPC rating. A property with a EPC rating of E50 can reach D60 rating with minimal insulation, depending on what insulation is chosen the you can expect around 10-15 points improvements in your EPC rating.
When we do joist celing insulation we cover the insulation and make sure the loft is a usable space we even have options that convert the loft into a great storage space.(224 words)